1. Field of the Invention
The present invention relates to an oil pan structure, and in particular, relates to an oil pan structure that can prevent overheating when an oil temperature is high by providing, at a lower portion of the oil pan, a cooling portion through which substantially an entire quantity of oil that is fed into an internal combustion engine passes, and that can quickly raise the oil temperature when it is low.
2. Description of the Related Art
In recent years, temperature control of oil that is used in lubrication of internal combustion engines has become important. This is because the temperature and the viscosity of oil are correlated, and the viscosity of the oil must be maintained within a constant range in order to maintain a constant oil film thickness. In addition, the oil that is discharged from the lubrication paths of the internal combustion engine during use normally acquires a temperature that is higher than a suitable temperature range, and thus cooling the oil so that the temperature thereof falls within the suitable temperature range before flowing back into the lubrication paths is being investigated (refer, for example, to Patent Document 1).
In Patent Document 1, an oil pan is disclosed that has a double-walled structure formed from an inner wall and an outer wall. In the oil pan, a slope portion inclining downward toward an oil strainer that is in the inner wall is formed at a portion of the inner wall, and a number of communication openings that communicate the inside portion of the inner wall and a space between the inner and outer walls are provided in the slope portion. In the oil pan, a circulation path of the oil is changed depending on a difference in the viscosity of the oil due to the oil temperature, whereby a rise in the oil temperature is hastened during warm-up, while a rise in the oil temperature is suppressed after warm-up.
However, in Patent Document 1, cooled is only oil that has flown between the inner and outer walls and come into contact with the outer wall. Oil that has been drawn back into the oil strainer without coming into contact with the outer wall is also present, and thus it is not possible to suppress a rise in the temperature of such oil.
Patent Document 1: Japanese Patent Application Publication No. JP-A-2004-218582